This invention relates to a method of improving the working properties of fluid system, e.g., hydraulic, lubrication, fuel, etc., which are contaminated mainly during operation with the cause of the contamination being unavoidable.
It is well known that the reliability and the longevity of both fluid systems themselves (hydraulic and fuel) and the machines they take care of (the lubrication systems of engines, compressors and others), in many respects, depend on the working properties of the used fluid.
These properties are determined by the presence of the solid, gaseous and liquid contaminants in the fluid, the fineness of the latters and the state of their dispersion.
The solid contaminants are the products of wear (metal filings, rubber, etc.) and oxidation of both the details (e.g. bearings, gears, seals) and the working fluid itself, or are the dust (the most destroying contaminant) from the atmosphere.
The intensity of the contamination from the atmosphere, e.g. in hydraulic systems (especially those of farm, road-making, construction and the like machinery), depends on fluid volume oscillations in their tanks when operating. These oscillations are basically dictated by the work of their hydraulic cylinders and accumulators.
The matter is not only that the solid contaminants are abrasive, cause wear and decrease (in many times) the term of fluid unit service, but they may wedge movable details (especially the plunger ones) and be the cause of the inoperativeness of automatic controls. As much as to hydraulic systems, this is true for fuel-feed engine systems, especially those of fuel-feed diesels and gas turbines. Of the latters, the problem particularly arises in road-vehicle gas turbines because the parts of such systems are many times smaller (in comparison with those of aircraft) with openings susceptible to blockage through dirt ingress and carbon deposit formation.
The gaseous contaminants (air, carbon dioxide, sulfur dioxide, water vapor, etc.) are absorbed from the atmosohere (as above) or from their internal source (e.g. incomplete combustion processes).
The unsolved gaseous contaminants deteriorate the pliability of fluid systems. their triggering, stability, and may cause inoperativeness.
Some gaseous contaminants (e.g. sulfur dioxide) form acids (causing corrosion) with water. Besides, oxygen solubility-in-fluid being higher than that of atmosphere air, the dissolved one contains 40-50% more oxygen. This intensifies the oxidation of the fluid and the metal details, and destroys the rubber ones.
Also, the gas forms foam decreasing oil lubrication ability and causing the corrosion of metal details, oxidation and other chemical reactions in the oil (because of bigger interface and more oxygen content). The stable foam, in time, forms viscous contaminants depositing on the detail surfaces. The forming of foam increases sharply when water is present (even at only 0.1%).
Gas is always present in fluids, at least in a dissolved form, and usually does not affect fluid mechanical properties. But vibration, decreasing pressure and heating give the gas off (even with foaming) and form the inoperative mixture instead of the former solution fitted for work. That is why the problem especially arises in fluid systems on vehicles when the systems remaining inoperative are subjected to jarring and vibration. This may aggravate starting such a hydraulic system or the fuel system (if there is an auxiliary engine).
Of fuel systems, the air problem is of particular importance in diesel ones, where the fuel is relatively viscous and therefore, there is the tendency for air to entrain into the fuel and to terminate fuel delivery to the combustion chambers.
As to liquid contaminants, the main representatives of those are water and fuel. The water in its vapor form comes into the "breathing" tank (as described above) and condenses when the temperature drops. The fuel may come into the lubrication system from combustion chambers or because of leakage, etc.
Because fuel is volatile, the effects of it are like those of the gaseous contaminants. The effect of the water contaminant has been described above.
The main known methods of fluid decontamination are the continuous removing of contaminants from the fluid by means of straining, filtering, absorption, gravitational displacement, magnetic, electrostatic and centrifugal separation, evaporating in atomized state, etc. Independent continuous or periodic purification is employed with full-flow and bypass (5-20% of the flow).
The mentioned methods and appropriate means are described in many sources (U.S. Pat. Nos.: 2,215,756; 2,268,653; 3,154,087; 3,233,652; 3,329,194; 3,356,182; 3,444,871 and others).
Common to all the known methods of decontamination is the quest for removing all contaminants from the fluid. Being unable to do so, filtration, for example, is assumed to be the most qualified if the size of the filtrating material calibration channel is less than the half of the minimum clearance in the sliding pair. Still, being difficult, it does not go beyond the full clearance. Besides, the fine mesh filters may clog and, in some areas, even become a repository for geological growth.